Galactic Center at Very High Energies Essay -- The Universe, Black Hol

Every time a mod messenger (different photon wavelengths or a different particle) has added to the list of observables loving to astrophysicists, the Universe has appeared under a new light it has revealed surprising features and triggered new questions, ultimately changing our understanding of fundamental physics and cosmology.Examples include the new dewy-eyed particles discovered in cosmic rays in the 30s and 40s, flavor oscillations from the solar and atmospheric neutrinos, or the revolutions brought by radio or X-ray astronomy. The last decade, a new branch of astronomy was born high energy and very high energy gamma-ray astronomy.Especially, 2OO4 was a very importand year for the gamma-rays astronomy. Firstly it was the year that marked the thirtieth aniversary of the discovery of the compact radio obtain Sgr A* (Balick and Brown 1974) which is now strongly believed to be the revelation of a super pickleive black hole of a mass of (3 imes 106 M odot ) that seats in the rot anional center of the Galaxy, according to the measurments of star motions near the Galactic Center (GC). Moreover it was the year that the first detective work of gamma-rays from a compact region of size (sim 10) around Sgr A* with the INTEGRAL (extitInternational Gamma-Ray Astrophysics Laboratory ) observatory in the energy rage from 20 to hundred keV (Belanger et al 2004) and with the HESS (High Energy Stereoscopic System) Cerenkov telescope array between 165 and 10 TeV (Aharonian et al 2004) took place. The detection of a high energy radiation source that appears to be pointlike and coincident with the Galactic Nucleus seems to be the reword of 30 years of observations. The GC is now observed also by the Fermi office observatory. When J.Co... ...i.e. within (sim 100 ) Schwarzchild radii of the black hole). This fact must be explained by any model for the TeV gamma-rays and it seems to support the scenario where the gamma-rays are assosiated with electrons accelarated by the pulsar wind nebula.However, protons may be accelarated close to the black hole, but be converted to gamma-rays only after travelling a significant distance away from the accelaration region (e.g. Atoyan n Dermer 2004 Aharonian n Neronov 2005 Ballantyne et al. 2007a). In the scenario presented by Ballantyne et al. (2007a), proton accelaration was assumed to occur at distances only (sim 20-30 ) Scwarzchild radii from the black hole (e.g. Liu et al. 2006). The particles would then diffuse away from the Sgr A* through the magnetized irritated ISM ? , until possibly colliding with the dense molecular gas in the circumnuclear disk.